1. Field of the Invention
The present invention relates to a photopolymerizable dental composition which is cured by irradiation with visible light. More particularly, the present invention relates to a dental composition which causes less coloration after curing. The composition of the present invention is used for dental filling materials, dental crown materials, artificial tooth materials, dental adhesives, dental surface coating materials, dental opaque materials, dental manicure materials, etc.
2. Description of the Related Art
Current dental treatments view aesthetic qualities as one of the most important elements. There is a strong requirement for the characteristics of dental materials to be such that the color of restorations resembles that of a natural tooth, and has a beautiful white color.
In actual treatment, a color tone is determined by comparing a color tone of the natural tooth of the patient with that of materials such as fillers. However, materials comprising a combination of a conventionally used visible light-photopolymerization catalyst and a polymerizable monomer displayed inferior aesthetic qualities since a color tone varies before and after curing, resulting in poor compatibility with a color tone after mounting in the oral cavity.
In the dental field, a visible light-polymerizable resin has been widely used. The disclosure of UK Patent No. GB1408265 resulted in broad application of a photopolymerization initiator therefor including a hydrogen abstracting initiator comprising an a-diketone compound and an amine compound, such as camphorquinone having a maximum absorption wavelength of 470 nm. However, a photopolymerization initiator comprising an a-diketone compound and an amine compound has problems such as drastic yellowing and change in a color tone of the cured article associated with the amine compound.
Acylphosphine oxide compounds disclosed in U.S. Pat. Nos. 4,265,723 and 4,298,738, and (bis)acylphosphine oxide compounds disclosed in U.S. Pat. Nos. 4,792,632, 5,721,292 and 5,965,776 show excellent photopolymerizability in an ultraviolet or near ultraviolet range and are therefore widely used in the photopolymerization industry field. Also, these compounds are less likely to cause yellowing of the cured article when compared with an a-diketone compound and an amine compound. However, there is a problem that yellowing is caused by interaction after curing depending on the kind of a polymerizable monomer.
Japanese Patent No. 2,629,060 reports a photopolymerizable dental surface coating material comprising dipentaerythritol hexaacrylate and an acylphosphine oxide compound. This patent reports that the photopolymerizable dental surface coating material has excellent thin-layer surface curability since it contains dipentaerythritol hexaacrylate and an acylphosphine oxide compound. However, there is a problem that curing caused by the dipentaerythritol hexaacrylate and the acylphosphine oxide compound causes browning of the cured article.